The editors of Sai Gon Tiep Thi (Saigon Marketing) newspaper terminated Huy Duc's contract on Tuesday, the newspaper's editor Tran Cong Khanh said. In addition to his work as a reporter, Duc wrote a popular blog, Osin.
Khanh said Duc's dismissal was linked to a blog post on the Cold War-era Berlin Wall, which divided the communist and Western sectors of the German city and which Duc referred to as "a Wall of Shame."
The blog post accused Vietnam's former communist ally the Soviet Union of imposing on Eastern Europe "a regime which deprived men of fundamental rights."
"I don't know if he wrote about other sensitive things," Khanh said.
Duc declined to comment when reached by telephone.
After the Vietnam War ended in 1975 the Soviet Union became Vietnam's main benefactor until the Soviet regime collapsed in 1991.
In a post Wednesday Duc confirmed he was "no longer a reporter of Sai Gon Tiep Thi." He had spent nearly four years at the newspaper.
Like all media in Vietnam, the newspaper is linked to the state. But Duc wrote that, even so, the press "must be the place to convey honest articles, analysis and criticism... articles that journalists believe serve society."
Other posts by Duc, a veteran journalist and former soldier, have criticised government responses to major issues including corruption, relations with China, and treatment of the media.
US ambassador Michael Michalak told reporters this week that he remained concerned about human rights in Vietnam, including efforts to crack down on the media and to "criminalise free speech."